Electric control circuit



Dec. 18, 1945. E, BNEN 2,390,982

ELECTRIC CONTROL CIRCUIT Filed Sept. 30, 1942 I5 Sheets-Shget 1 Fig. la.

8/48 V OL 7'4 65 PREHEAT rm:

Inventor:

Maurice E. Bivens,

H mttornea.

1945- M. E. BIVENS ELECTRIC CONTROL CIRCUIT 3 Sheets-Sheet 2 Filed Sept. 30. 1942 Fig. lb.

COOL 7/ME R I62 HEAT 7mm 443 WELD 7mm or; T/MEH Inventor Maurice, E. Bivens, b M MW His Attorneg.

Patented Dec. 18, 1945 ELECTRIC CONTROL CIRCUIT Maurice E. Bivens, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application September 30, 1942, Serial N 0. 460,240

22 Claims.

My invention relates to electric control circuits, and more particularly to improved electric valve control circuits for effecting the transfer of current to a load circuit in accordance with a predetermined pattern.

In the application of electric valve control circuits to industrial processes, such as resistance welding, there has arisen the need for improved control circuits for energizing the load with a predetermined current pattern and particularly to improved circuits having greater flexibility with respect to the current variation that may be obtained during different intervals or component parts of the complete pattern. It is also desirable to increase the flexibility of the apparatus with respect to the different types of current variations or patterns for which the system may be adjusted to increase the applications for which the equipment is suited. In accordance with the teachings of the present invention, I provide such a system which embodies means for selecting one of a. number of available current patterns and also providing for the adjustment of the apparatus to permit the independent adjustment of current magnitude supplied to the load circuit at various intervals in the selected pattern as well as to control independently the rate of change of current from one magnitude to another during the pattern.

It is an object of my invention to provide a new and improved electric valve control system.

It is another object of my invention to provide a new and improved electric translating apparatus for effecting the energization of a load circuit in accordance with a selected one of a number of current patterns.

It is another object of my invention to provide a new and improved electric valve control circuit for efiecting the energization of a load circuit in accordance with a current pattern which may be preselected and in which the extent of current variation and length of time interval of the various portions of the pattern may be adjusted independently.

It is still another object ofiny invention to provide a new and improved resistance welding system which may be readily adjusted to accommodate the system for a wide variety of work with respect to composition or dimensions of the work iece.

In accordance with an illustrated embodiment of my invention a welding transformer is energized from an alternating-current supply circuit through electric valves of the immersion ignitor type which are reversely connected in parallel,

The periods during which the welding transformer is energized are determined by a switching device connected in circuit with the ignitors and which is controlled by timing means to complete the circuit of the ignitors and the control valves therefor for the intervals during which current is to be supplied to the load circuit. The magnitude of the current supplied to the welding transformer is controlled by phase controlling the electric valves, which is in turn effected by means of a bias control voltage impressed on the control members of a pair of control valves and which is varied in accordance with the variation in current magnitude of the selected current pattern to be supplied to the welding transformer. The bias voltage is a variable voltage existing between a reference point and one terminal of a capacitor having charging circuits which are altered at various points in the welding pattern to effect the difierent types of current variation desired during different intervals of the total current pattern or, for other patterns, the bias voltage remains constant for a portion of the pattern and then is abruptly changed to a second valve dependent upon the setting of a variable tap on a voltage divider under the control of a timer. The charging of the capacitor is also utilized to determine the duration of certain of these intervals in cooperation with additional control electric valve means and electromagnetic switching devices. In general, the system contemplates a current pattern which may comprise a preheat period, a welding period, an on period, and a postheat period in which the initial value of preheat current, the magnitude of the welding current, and

the final value of postheat current are all independently adjustable and in which the duration of the preheat, weld, off, and postheat periods are also independently adjustable. The system also contemplates a gradual variation of current magnitude, either increasing or decreasing during either the preheat or postheat periods. By selectively operating certain manual switches, it is possible to alter the pattern so that the magnitude of current during each of the periods is of a constant magnitude and to decrease the off period to zero if desired. In the above description, reference has been made to preheat, weld, ofi, and postheat periods. In this description, it has been assumed that the entire current pattern takes place with the electrodes stationary to accomplish one weld. It is also possible to utilize these current patterns particularly if the off period is reduced to zero to accomplish a seam weld in which the current gradually increases, is

maintained constant, and then gradually decreases or, in accordance with another pattern,

remains constant at one value for a period, changes to another value for a second period, and alters again to a third value for a third period. In accordance with another pattern, the current gradually decreases during the first period, is maintained at a constant value for a second period, and gradually increases in value for a third period. Thus, the system is very flexible, providing for almost any current variation desired over a complete pattern including a plurality of intervals or periods of different types of current variation.

In accordance with the illustrated embodiments, provision is also made for effecting intermittent energization of th load during any one of the plurality of periods making up a complete pattern. For example, if a complete current pattern represents a single weld with the electrodes stationary, the intermittent energization during each of the periods may be referred to as pulsation Welding. This intermittent energization is accomplished 'by means of electronic timers which operate the switching means in the control member circuit of the main electric valves.

My invention will be better understood by reference to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. In the drawings Figs. 1A and 13 considered together are a schematic representation of one embodiment of my invention, and Fig, 2 illustrates various current patterns which may be supplied to the load circuit of the arrangement shown in Figs. 1A and 13, together with a schematic representation of the operating conditions of a number of the electromagnetic switching devices at various times during the current pattern.

Referring now to Figs. 1A and 1B of the drawings, I have shown my invention embodied in an electric valve control circuit for energizing a load, such as a welding transformer Ill from an alternating current supply circuit H in accordance with a selected one of a plurality of current patterns. The flow of current from the supply circuit to the welding transformer is controlled by a pair of electric valves l2 and [3 which are reversely connected in parallel between the supply circuit and the primary winding M of the transformer Ill. Electric valves l2 and I3 may be of any of the types well known in the art and, as illustrated, each comprises an anode l 5, a cathode l6 of conducting liquid such as mercury, and an immersion ignitor type of control member l1.

As'is well understood by those skilled in the art, the electric valves l2 and I3 illustrated in the drawings are of the type requiring the passage of a predetermined minimum current to the control members I! thereof to initiate conduction of the electric valves. As illustrated, the passage of current to the control members I! of the electric valves l2 and I3 is controlled by the firing or trigger valves l8 and I9, which are preferably' of the type utilizing an ionizable medium and each comprising an anode 2!), a cathode 2 I, a shield grid 22, and a control member or grid 23. The electric valves I8 and I9 are reversely connected in parallel and have the anode-cathode circuits thereof energized in accordance with the anode voltages of the electric valves [2 and I3, respectively. As is readily seen from the drawings, the anode-cathode circuit of electr c val e.

I9 is completed from the anode of electric valve l3 through a unilaterally conducting device 24, such as a dry rectifier, a conductor 24a, switch 25, a conductor-25a, the normally open contact 26a of an electromagnetic switching device 26 having an operating coil 21, a unilaterally conducting device 28, the control member H to the cathode of the electric valve [3,, From an inspection of the drawings, it will be seen that when electric valve [3 is nonconducting, the anode-cathode voltage thereof is impressed on the anode-cathode circuit of the control or firing valve I9. The anode-cathode circuit of the control valve I8 is completed from the anode of electric valve I2 through a unilaterally conducting device 29, the normally open contact 2805 of the switching device 26, conductor 25a, switch 25, conductor 24a, a unilaterally conducting device 30, and the control member l5 of electric valve l2 to the cathode [5 of the electric valve 12. Inasmuch as the contact 260; is in the anodecathode circuit of both of the control valves l1 and 18, it is apparent that no current for initiating discharge of electric valves l2 and I3 may be conducted through the ignitor type control members l5 when contact 26a is open. This contact, accordingly, provides means for determining the periods of energization, and deenergization of the welding transformer.

In order that the time in the anode-cathode voltage of electric valves l2 and I3 may be controlled to control the voltage or root-meansquare value of current supplied to the welding transformer, I provide an improved control cirthe control valves l8 and 19. The control member of each of these valves is energized by the excitation circuits illustrated generally by the numerals 3| and 32, respectively, which are idensame reference numerals will be applied to corresponding parts of both of the excitation circuits. Referring to excitation circuit 3| for energizing control member 23 of electric valve l8, a source of hold-off alternating-current voltage is provided by the secondary winding 33 of a transformer 34 having the primary winding 35 energized from. a supply of alternating-current control voltage provided by conductors 36 and 31 which are energized from the alternating-current supply circuit II by means of a voltage-dividing reactor 38. The secondary winding 33, which provides the hold-off voltage, is connected in series with the secondary winding 39 of a transenergized to provide a peaked Wave form voltage for overcoming the effect of the hold-off voltage of winding 33 to render electric valve l8 conductive at the desired instant in the anodecathode voltage wave of the valve 12 in a manner which will be described more in detail at a later point in the specification. The circuit of the control member 23 includes a self-biasing resistor 42 and parallel connected capacitor 43. The circuit to the cathode of the electric valve is is completed from a terminal of the transformer winding 33 through conductor 44 which is also connected with the shield grid 22 to main tain the same at cathode potential. Filter capacitors45 are connected between the cathode and opposite side of the biasing resistor to eliminate the effect of transients on the excitation circuit.

' A filter capacitor 46 is also connected across the" transformer winding 33. A secondary winding 41 cuit for controlling the control members 23 of tical so that only one will be described and the former 40 having a primary winding 41 which is,

of thetransformer 34 provides asource of cathode heating current for the valves 18 and H.

The self-biasing means including resistor 42 and capacitor 43 together with the hold-off altermating-current voltage of transformer 33 provide means for normally rendering electric valves l8 and I 9 noncond-uctive. As mentioned previously, a tum-n voltage is introduced in the excitation circuits 3| and 32 by means of the transformer secondary windings 39. In order to determine the instant that electric valves l8 and I9 are rendered conductive and, consequently, the instants at which electric valves I2 and 3 are rendered conductive, the transformer windings 4| are energized in timed relation with the anode-cathode voltage supplied to electric valves I2 and I3 in accordance with the magnitude of current which is to be supplied to the load circuit for the particular pattern of welding current for which the system has been adjusted. .In order to control the electric valves I8 and I9, I provide a pair of electric discharge valves 48 and 49 for energizing the primary windings 4| of the transformers 46 of the excitation circuits 3| and 32. The electric valves, as illustrated, are of the type utilizing an ionizable medium and each comprises an anode 56, a cathode and a control member or grid 52. A source of alternatingcurrent voltage for energizing the anode-cathode circuits of electric valves 48 and 49 is provided by a mid-tapped secondary winding 53 of a transformer 54 having the primary winding 55 thereof energized from the alternating-current control voltage supply 36, 31 through the normally open contacts 56 of an electromagnetic switching device 51. The cathodes of the electric valves 48 and 49 are electrically connected together and this common connection is connected by conductor 58 through the primary windings 4| in series to the midtap of winding 53, the end terminals of which are connected through suitable current-limiting resistors 59 to the anodes 56 of the electric valves 48 and 49, respectively. The control members 52 of electric valves 48 and 49 are each energized by an alternating-current component of voltage supplied by resistors 66 and 6| and a direct-current component of voltage or bias impressed across conductors 52 and 63 by a control circuit to be described in detail at a later point in the specification. The voltage impressed across resistors 66 and 6| preferably lags the voltage impressed on the anode-cathode circuit of electric valves 48 and 49, respectively, by substantially 90 electrical degrees and is derived from the alternating-current control voltage supply 36, 31, by means of a transformer 64 having the primary winding 65 thereof connected between an intermediate point on the voltagedividing reactor 38 and the common terminal of a series connected resistor 66 and capacitor 61 which are energized by the voltage of the alternating-current supply 36, 31. An adjustable tap 68 on the resistor 66 provides means for adjust ing the phase of the alternating-current voltage impressed on the transformer primary winding 65. The secondary winding 69 of the transformer 64 is provided with a midtap which is connected to the common terminal of resistors 69 and GI and also to the conductor 62. The end terminals of transformer winding 69 are connected respectively with the end terminals of the resistors 66 and 6|. The control members 52 of electric valves 48 and 49 are connected with resistors 66 and BI, respectively, through suitable currentlimiting resistors 16 by means of adjustable taps The circuit between the control members of valves 48 and 48 is completed from the conductor 63 through transformer windings 4| and condoctor 58. From the previous description, .it will be seen that the control members of electric valves 48 and 49 are energized in accordance with the alternating-current voltage appearing across a portion of resistors 66 and 6|, respectively, and the voltage impressed across conductors 62 and 63. Thus, it is seen that the time in the anodecathode voltage of electric valves 46 and 49 at which they are rendered conductive may be -controlled by controlling the voltage impressed on conductors 62 and 63.

:In the previous description, it has been pointed out that the time of conduction :of valves 48 and 49 controls the electric valves |2 and I3 thro transformers 46 and electric valves 18 and I9. The control circuit for controlling the voltage impressed on conductors 62 and 68 will now be described. The source of energy for this control circuit is provided by the direct-current control voltage supply comprising conductors 12 and I3 which are energized by the output of a full wave electric valve rectifier comprising an electric valve device 14 having two discharge paths which areenergized by the mldtapped secondary winding 15 of a transformer 16 having the primary winding 11 thereof energized from the alternating-current control voltage supply 36, 31. The output of the electric valve rectifier is filtered by a series inductive impedance l8 and parallel capacitor 19 before it is impressed upon the direct-current supply conductors l2, 13. A switch 88 is preferably connected in one of the supply lines of the direct-current circuit and, as illustrated, is connected in the conductor 12. The transformer 16 is provided with secondary windings 8| for heating the cathodes 5| of electric valves 48 and 49.

Before proceeding further with the description of the system of the illustrated embodiment of my invention, brief reference may be had to Fig. 2 of the drawings to obtain a better understanding of the type of control to be accomplished by the remainder of the system which determines the magnitude of the load current supplied as well as the duration of the four periods into which the current pattern is divided; namely, the preheat period, weld period, off period, and postheat period.

Referring particularly to Fig. 2, pattern A, it will be noted that the magnitude of the current steadily increases during the preheat period, is maintained at constant magnitude during the weld period, and gradually decreases from the weld current magnitude to a final value at the end of the postheat period. The circuit for controlling the variations in magnitude of the current as well as the duration of the preheat and postheat periods, will now be described.

Referring again to Figs. 1A and 113, it will be noted that the conductors 6.2 and 63, which impress the control voltage on the control members of electric valves 46 and 49 to control the ma nitude of the current supplied to the welding transformer by electric valves |2 and I3, are connected to the movable contacts 82 of a reversing switch, the fixed contacts of which are connected with conductors 83 and 84. It will also be readily appreciated that the voltage appearing between conductors 83 and 84 may be impressed on the conductors 62, 63 in opposite senses by moving the movable contacts 82 from one extreme position to the other. The conductor maybeselectively connected with-conductor 85 for conductor 86 by the single-pole, double-throw switch 81. Thus, with switches 82 and 81 in the position shown, the voltage impressed on conductors Hand 63 is determined by the voltage of conductors 83 and 85. The conductor 83 is mailitained at a voltage intermediate the direct-current control voltage conductors 12, 13 determined by the position of an adjustable tap 88 on a'voltage-dividing resistor 89 which is connected in series with resistor 90 across the direct-current control voltage supply 12, 13. The conductor 85 is connected by conductors 9| and 92 and a switch 93 to one terminal of a'capacitor 94, the other terminal of which is connected to the negative side 12 f the direct-current control voltage supply. Thus, it is seen that the voltage of conductor 83 may be adjusted to a predetermined value between the voltage of conductors 12,13 of the direct-current supply voltage and that the conductor 85 has a voltage positive with respect to the negative direct-current line 12 by an amount dependent upon the charge on the capacitor 94. A capacitor 94a and a switch 9311 may be connected in parallel with switch 93 and capacitor 94 to provide an extended range of operation. In order to provide adjustable voltages intermediate the voltages of the direct-current supply conductors 12, 13 which may be selected in advance to determine the condition of charge of the capacitor at different periods of the cur rent pattern, such as beginning of reheat period, end of preheat period, weld period, and end of posthead period, I provide voltage dividing resistors 95 and 96 connected in series with a re-' sistor 91 across the direct-current supply lines 12, 13. Connected between adjustable points on resistors 95 and 96 are resistors 98, 99, and I00. An adjustable tap IOI on resistor 98 establishes the initial charge on condenser 94 and, therefore, determines the value of current transmitted to the load circuit at the beginning of the preheat period as will be better understood by tracing this charging circuit. Starting with the tap IOI on the voltage dividing resistor 98, the circuit extends by way of a conductor I02, contact I03 of a manual switch I04, conductor I05, normally closed contacts I06a of an electromagnetic switching device I06, having an operating coil I01, conductor I08, a current-limiting resistor I09,,control member H0 and cathode III of an electric discharge device II2, conductor II3, conductor 92, switch 93, capacitor 94 to the negative line 12 of the direct-current control Vo1tagesupply. Thus the capacitor 94 charges to the voltage between the direct-current supply line 12 and the tap I0l through the control-member-to-cathode circuit of the electric valve II2 to establish the initial charge on capacitor 94 and thereby establish the magnitude of the load current at the beginning of the preheat period. Inasmuch as this charging circuit of capacitor 94 includes a unilaterally conductive path from the control member to the cathode of valve I I2, it is necessary that capacitor 94 be discharged prior to the establishment of the circuit for charging the capacitor to the initial preheat setting. This is accomplished by a discharge circuit for capacitor 94 including resistor I I3a and the normally closed contacts [066 of switch I96. The electric valve H2 is preferably of the type employing an ionizable medium and comprises in addition to the control member IIO and cathode III an anode H4. The anode-cathode circuit of the electric member or grid I33.

valve H2 is energized from a secondary winding H5 or the transformer 54 through a circuit including in series a unilaterally conducting device II 6, conductor II1, normally open contacts II8a of an electromagnetic switching device II8 having an operating coil II9, the operating coil I20 of an electromagnetic switching device I2I, conductor I22, resistor I23, the anode-cathode circuit of electric valve I I2, conductor I24, conductor I25, to the other terminal of the transformer winding I I5. 7 The preheat time, or first interval of the current pattern, is determined by the time required for the capacitor 94 to charge from its initial value determined by the position of the adjustable tap IOI to a final value determined by the position of an adjustable tap I26 on the voltage-dividing resistor 99, which also determines the magnitude of the current during'the welding interval as will be described more in detail at a later point in the specification. The capacitor 94 charges during the preheat period from the direct-current supply 12,13, through conductor 92, conductor 9I, conductor I21, normally closed contacts II'8b of the electromagnetic switching device II8, the normally open contacts I06b of the switching device I06, conductor I28, and an adjustable resistance I29. When the capacitor 94 charges to a value dependent upon the setting of the adjustable tap I26 on the voltage dividing resistor 99, the second interval of the current pattern or the welding interval is initiated by the initiation of conduction of an electric valve I30 which is similar to the electric valve I I2 and comprises an anode I3I, a cathode I32, and a control The cathode I32 of the electric valve is connected with theadjustable tap I26 by means of a conductor I34, a conductor I35, a conductor I36, the movable contact I03a on manual switch I04, and conductor I31. The con-' trol member I33 of electric valve I30 is connected by conductor I38, resistor I39, conductor II3, conductor 92, and switch 93 to the positive terminal of the capacitor 94. The anode-cathode circuit of the electric valve I30 is energized from a fourth winding I40 on the transformer 54, one terminal of which is connected to the anode of the valve I30 through a unilaterally conducting device I4I, conductor I42, normally closed contacts I I8c of an electromagnetic switching device IIB, the operating coil I43 of an electromagnetic switching device I44, conductor I45, and resistor I46. The other terminal of the transformer winding I40 is connected with the cathode of electric valve I30 through conductor I41, conductor I35, and conductor I34. The cathodes of electric valves 14, H2, and I30 may be heated by energy supplied by the windings I48 of the transformer 16. The voltage of conductor is then maintained at a voltage determined by the setting of the tap I26 or the weld heat adjustment until the termination of the weld interval, or period, which is determined by means of an electronic timer illustrated generally by the numeral I49 and bearing the legend Weld timer which operates to energize the operating coil I50 of an electromagnetic switching device I5I at the end of the weld period. If the system is adjusted for a current pattern having an off period, such as the pattern illustrated in Fig. 2A, the termination of the welding interval and closure of the contacts I5I b of relay I5I initiates an ofi period by starting the timing operation of another electronic timer illustrated generally by the numeral I52 and bearing the legend Off timer. Theoff ,ence voltage.

timer efi'ects the energization of the operating coil I53 of electromagnetic switching device I54 at the end of the oiT period and closes the normally open contacts I54a to establish a shunt circuit around the contact I55a of the manual switch I55 and completes the energizing circuit for the electromagnetic switching device I I8 from the alternating-current supply lines 36 and 31 through the manually operable initiating switch I56. The operation of switching device I I8 closes normally open contacts M to complete the discharging circuit for capacitor 94 for the postheat interval during which time it discharges charges from the voltage of the movable tap I26 of voltage divider 99 to the movable tap I51 of the voltage divider I00. This discharging circuit of the capacitor 94 may be traced from the negative side 12 of the direct-current circuit which is also the negative terminal of capacitor 94 through the variable resistor I58, conductor I59, contacts II8d, conductor I21, conductor 9|, con- .ductor 92, switch 93, to the other terminal of capacitor 94. When the capacitor 94 reaches the voltage of the adjustable tap I51 of voltagedividing resistor I00, electric valve 4 is rendered conductive; inasmuch as the cathode thereof is connected with the positive terminal of the capacitor 94 and the control member thereof is, at this time, in the current pattern connected with the tap I51. This-latter circuit may be traced from the tap I51 of the voltage-dividing resistor I through contact I03-b of switch I04, contacts 11% of the switching device I I8, the contacts l06c of the switching device I06, conductor I08, and resistor I09. Conduction of electric valve 1 I2 energizes the operating coil I20 of switching device 'I2I to open the contacts I2'Ia and terminate the current pattern by interrupting the circuit of coil I01 of switching device I06.

In the above description, the control of the electric valves I2 and I3 by controlling the bias impressed on conductors 62 and 63 has been described with the manual switch 81 connected 'to conductor 85. If manual switch 81 is connected with conductor 86 the voltage impressed on the conductors 62 and 63 then becomes the voltage between conductors 83 and 86. As previously mentioned, conductor 83' is connected to an adjustable point on resistor 89 to determine a refer- The voltage of conductor '86 is varied to determine the current pattern. "By reference to the drawings, it will be noted that conductor '86 is connected to the adjustable tap IOI of voltage-dividing resistor 98 through normally closed contacts I44a of switching device I44; 'to the adjustable tap I 26 of voltage-dividing resistor 99 through normally open contacts I-4'4b of the switching device I44; and to the adjustable tap I51 of the voltage-dividing resistor I00 through the normally open contacts H81 of the switching device I I8. Thus, the voltages between conductor 83 and the taps IOI, I26, and I51, respectively, of the voltage-dividing resistors 98, 99, and I08 are impressed on the conductors 6.2 and 63 during successive intervals, namely, the preheat, weld, and postheat intervals of the current pattern illustrated in Fig. 2B in accordance with the operation of the electromagnetic switching devices H8 and I44.

From the foregoing description, it'isseen'that, when the apparatus is set for either pattern B .or D, the bias voltage impressed on the control members of electric valves '48 and 49 ischanged abruptly at the ends of the different intervals to the values established by the voltage-dividing re- :timing resistors I29 and I 58.

sistors 98, 99 and I00. Since the settings of the taps on these resistors also ellect the length of the preheat and postheat periods as a result of establishing the initial and final charge on the capacitor 04 for thes intervals, it is apparent that adjustment of current magnitude for any of the periods will require a readjustment of the In order to provide that the timing during preheat and postheat periodsshall be entirely independent of the current magnitude durin current patterns such as illustrated in Fig. 2, patterns B and D, I provide means for determining the condition of charge of the condenser 94 at the beginning of preheat, end of preheat and end of postheat independently of the magnitude of the current supplied during these intervals by the manual switch I04 which,

when moved to its right-hand position, connects the control member of electric valve II2 with an adjustable tap I60 on resistor through one path containing normally closed contacts 'I06a of electromagnetic switch I06 and a parallel path through normally open contacts H80 and I06c in series of switching devices H8 and I06, re :spectively. The cathode of the control electric valve vIJlIIis connected directly with an adjustable tap m 011 the resistor as through contact I-03a, conductor I36, conductor I35, and conductor I34. In this way, the charge on the condenser at the beginning of preheat, the charge on the condenser at the end of preheat which is also the charge on the condenser 84-at the end of the weld .or off period, and the charge on the condenser 94 at the .end of the postheat period are established ,ence has been made to electronic timers I49 and 152 whichdetermine, respectively, the length of the welding period and the off period of current patterns .A to D of Fig. 2, inclusive. Heat and .cool timers 1:62 and I63, respective y, are also provided to effect intermittent energization of the load circuit during any one of the three periods of energization of the current pattern illustrated. Thlsadapts'the system for what is termed pulsation welding when the electrodes are stationary throughout .the current pattern as they are when the system isv being used for spot welding.

Electronic timers I49, I52, I62, and I63 are energized from an alternating-current supply which, as illustrated, comprises conductors I64 and .165 energized from the secondary winding I66 of axtransiormer 161, the primary winding 4680f which is energized from any'suitabl source, whichmaybe the alternating-current supply cir-' cuit 11. Each of the timers comprises an electric discharge valve 169 preferably of the type utilizing an ionizable medium, such as a gas or vapor, and comprising an anode I10, a cathode I;1I, a shield grid I12 and a control member of grid I13. In each of the timer circuits, the shield grid is connected directly to the cathode. The control member is-energized from an adjustable tap I14 on a voltage-dividing resistor which is connected in series with resistors I16 and I11 across the lines I64 and I65. The circuit between the adjustable tap and the control member includes resistors I18 and I19 which are paralleled by a capacitor I 89. Manually operable switch I8I connected in parallel with resistor I18 provides means for changing the range of operation of the timers. A current-limiting resistor I82 is connected in series with each of the control'members. The circuit between the cathode of the electric valves I69 of each of these timers is connected with one of the alternating-current lines I64 or I 65 through a switch which is closed to,

initiate the timing operation. Before the initiating switch is closed, the capacitor I80 is charged to a value dependentmpon the position of the adjustable tap I14 by grid rectification. Upon closure of the switch in the cathode circuit, no further grid rectification takes place and the electric valve becomes conductive an interval of time after clossure of the switch in the cathode circuit dependent upon the constants of the circuit including the voltage ofthe adjustable tap I14 and the time constant of the discharge circuit of capacitor I 80. A timer circuit of this type is claimed and more fully described in Patent No. 2,171,347- Schneider, dated August 29, 1939, and assigned to the same assignee as the present invention. The initiating circuits or switches and the operated relays of the timers I49, I52, I62,.and I63 are arrangedto provide a particularsequence of operation in th illustrated embodiment of the present invention and will now be considered individually in more detail. 7 7

Referring now to the weld time I49, the anode I10 of the valve I69 thereof is connected to the conductor I65 through a resistor I83 and the operating coil I50 of the electromagnetic switching device II. The cathode 9f the electric valve of the timer I49 is connected with conductor I65 through a resistor I81 and to the conductor I64 through a pair of parallel circuits,-

anode I of the electric valve I69 thereof connected with conductor I65 through a resistor I86 and the operating coil I53 of an electromagnetic switching device I54. The cathode of the electric valve is connected to the conductor I64 through the normally closed contacts ,I55b of the manual switch I55 and two parallel circuits, one of which includes the normally open contacts I5Ib of the switching device I5I and the other of which includes the normally open contacts IIBg .of the switching device H8. The cathode of the electric valve I69 of the timer I52 is also connected with the conductor I65 through resistor I84.

The heat timer I62 is connectedin essentially the same manner as the weld timer I49 with the anode I1 Il of the electric valve I69 thereof connected to the conductor I65 through a resistor I88 and the operating coil I89 of an electromagnetic switching device I90 and the cathode thereof connected with the conductor I65 through resistorISI, The initiating circuit for the timer I62 or the connection between the cathode of the electric valve I69 thereof and the conductor I64 is arranged to be selectively completed by the operation of different combinations of a plurality of electromagnetic switching devices. By reference to the drawings, the circuit of the cathode of the electric valve I69 of the timer I62 may be traced; through normally closed contacts I92a of an electromagnetic switching device I92 having the operating coil I93 thereof energized in accordance with the operation of the cool timer I63 to a conductor I94. From conductor I94, the circuit may be tracedeither through the normally open contacts 26b of the switching device 26 or the normally open contacts I921) of the switching device I92 to conductor I95 through one of three parallel circuits to the conductor I65, the first of which includes the normally closed contacts I5Ic of the switching device I5I, the second of which includes the normally open contacts I540 of the switching device I54, and the third of which includes the normally open contacts I550 of manual switch I55. Conductor I is connected to the conductor I64 through the normally open contacts I96d of the switching device IGB. It will be noted that the energizing circuit for the operating coil 21 of the switching device 26 starting with conductor I64 includes the same contacts as the initiating circuit for the heat timer until the conductor I94 is reached. From conductor I 94, the circuit of coil 21 is completed to conductor I65 through the normally closed contact Ia of the switching device I90 controlled by the heat timer I62. A series-connected resistor I96 and capacitorv I91 between conductor I95 and one terminal of the coil 21 of the switching device 26 provide 'means for suppressing transients set up by switching operations in the circuit of coil 21. I

The circuit of the cool timer is somewhat different from the circuit of the other timers in order to insure that the system will always operate to provide a heat period first when adjusted for pulsation welding. The anodecathode circuit of the electric valve I69 of the cool timer is reversed with respect to the supply conductors I64 and I65. By reference to the drawings, it will be noted that the anode of electric valve I69 of timer I63 is connected with conductor I64 through the contacts I06d of switching device I06, conductor I85, the operating coil I93 of switching device I92, and'resistor I98. The cathode is connected to conductor I85 through a resistor I99 and to the conductor I65 through the normally closed contact 260 of the switching device 26. From a consideration of this circuit, it will be seen that the anode-cathode circuit of the, electric valve of the cool timer is completed through the normally closed contacts 26c of the switching device 26 before the contacts I06d are closed in response to a closure of the weldinitiating switch I56. This insures that the cool timer will be in the timed-out condition initially and permit a period of heating to start immedately after closure of the weld-initiating switch when the system is adjusted for pulsation welding. As soon as the switching device 26 operates to initiate a period of energization of the load,

circuit, the contact 290 is opened and the cool timer is reset.

As previously mentioned, the heat and cool timers I62'and I63 are rovided to eiTect pulsation welding or, in other words, intermittent energization of the load circuit during any one of the periods of the. current pattern being supplied to the load circuit. In order to render itpossible to provide pulsation or regular welding during any one of theintervals, I provide means for selectively disabling both the heat and the cool timers during any one of the periods. switches 200, MI, and 202 are connected in series and across the contact I96a, controlledby the Manual Y escapee heat timer, by conductors 203 and 204. Short circuiting of contact 100a prevents the heat timer from interrupting the circuit of the operating coil 2! of switch 26 and, in this way, prevents the opening of the contacts 26a in the circuit of the control members of the main electric valves I2 and I3 and also prevents the closing of the contact 260 which would start atiming period of the cool timer I 63. The selective short circuiting of the contact 'I90a during dif ferent periods of the current pattern to be supplied to the load is accomplished by contacts on the switching devices H8 and I 44 which shunt different ones of the manual switches 200 to 202, inclusive. As seen from the drawings, the normally closed contact II8h of switch H8 is connected in parallel with manual switch 202 and the normally open contact II8i of this switch is connected in parallel with manual switches 200 and 20! in series. The normally open contact 441 of switching device 144 is connected in parallel with the manual switch 200 and the normally closed contact I4 Ie is connected in shunt with the manual switch 20!. If it is desired'to provide pulsation welding during the first interval of energization of the load-circuit which has been designated the preheat period in Fig. 2. switch 200 is opened and the shunt circuit around the contact I90a is open as long as the operating coils of both switching devices H8 and I44 are deenergized. As will become more apparent from the operation of the system as a whole, this condition exists only during the preheat period. Similarly, if pulsation welding is desired during the weld period, switch 20! is opened and switches 200 and 202 closed. This will open the circuit shunting contact ISO-a and thus disable the heat and cool timers when contact I446 is open and before contact I'I8i is closed by operation of switching means I I8. As will be explained in more detail later, this condition occurs only during the weld period. Similarly, if manual switches 200 and '20! are closed and manual switch 202 opened, contact I90a will be shunted at all times except when contact I I8h is opened. This occurs only during the po'stheat period. Thus the switches 200,20I, and 202 and the contacts I44d, I44e, Biz, and H82 provide means for disabling the heat and cool timers I62 and I63, respectively, for any of the periods of energization of the load circuit.

In order to insure that the off-period timer will control the length of the off period even though the cool-period timer is set for a longer period than the off-period timer and is not disabled by the position of switches 200 to 202, inclusive, I provide means for insuring that the cool timer I63 times out immediately after the oil-period I52 times out. This is accomplished by completing a low-impedance path in shunt with the capacitor I80 of cool timer I63 by means of the normally open contact I54b on the switch I54 which is operated when the cool timer times out. The resistance element 205 connected in the shunt circuit is of relatively low value to discharge capacitor I80 as rapidly as possible with out damaging any of the circuit elements. A normally closed contact 87' on relay I I8 is connected in series with this shunt circuit to permit the cool timer to function during the postheat period if switch 202 is opened.

Although a detailed description of the operation of the various parts of the illustrated embodiment of my invention has been included with the foregoing description of the elements of the system, it is believed that a consideration of the operation of the system in general when adjusted for diiferent heat patterns will further bring out the features and advantages of the present invention. A table showing the condition of the various relays of the system at any time during the current pattern has been shown in connection with Fig. 2. In this table, a heavy line has been used to indicate that the operating coil of the relay is energized and that the relay has operated. In the case of the relay controlled by th timers, the dotted line has been shown to indicate the interval which the timer is measuring and the solid line indicates the period during which the relay of the timer is energized. After the alternating-current supply circuit II has been energized for a time sufficient to bring the filaments of all of the electric valves to operating temperature, the switches 25 and may be closed. It will be understood that a time-delay relay may be used for thispurpose. Closure of the switch 80 operates the relay 5! to close the contact 56 thereby to energize the anode-cathode circuit of electric valves 48 and 49 and electric valves H2 and I30. 'The operation of the system will now be described when the switches are adjusted to supply to the load circuit the current pattern illustrated in Fig. 2A. Manual switches 82,81, and I55 are in the position illustrated in the-drawings and switches 200, 20!, and 202 are closed. The capacitor 94, which provides the unidirectional control voltage for controlling the magnitude of the "current supplied to the load circuit, is charged to a. value dependent upon the setting of the 'adjustable tap I0! on the preheat voltage-dividing resistor 98. The discharge circuit across capacitor 94 including the resistor II3a insures that the charge on the capacitor is determined'by the tap I0! in the event that the residual charge on the capacitor from a previous operation is greater than would result from the setting oil the tap I0!. This provision is necessary since the charging circuit for the capacitor to the voltage determined by the tap I0! includes a unilaterally conducting path from grid to cathode of the electric Valve II2. If, now, the initiating switch I56 is closed, the operating coil I0! of the relay I06 is energized'to open contacts 106a and I06e and to close contacts I06b, I060, and I06d. Opening of contact I06e opens the discharge circuit for capacitor 94 including the resistor HM and the opening of contact I06a in the circuit of the control member of electric valve II2 interrupts the charging circuit of the capacitor 94 through which the capacitor has charged to a voltage dependent upon the setting of the tap I0! on the preheat resistor 98. C10- sure of contact I060 partially completes a circuit between the control member of the electric valve H2 and the adjustable tap I'5I on the postheat resistor I00. This circuit is completed at a later point in the current pattern by operation of the relay IIB. Closure of contact I06d of the relay I06 connects the supply line I64 of the alternating-current control voltage supply to the conductor I85. This impresses anodecathode voltage on the electric valve of the cool timer I63. As previously mentioned, the cool timer is initially in timed out condition so that the relay I 92 controlled by the cool timer I63 picks up immediately upon closure of the contact I06d of relay I06. The closure of these latter two contacts completes a circuit for the operating coil 21 of relay 26 through normally closed contact I'5Ic of the weld timer relay II and the contact I99a of the heat timer relay I99. This picks up relay 26 to move contacts 26a and 26b to closed positions and to open contact 260.

Closure of contact 26b establishes a holding circuit for the coil 21 in shunt with the contact I92b of the cool timer relay I92. Opening of contact 260 opens the anode-cathode circuit of the electric valve I69 of the cool timer I63 to reset the same. The closure of contact. 26a

completes the circuit between the immersion igpreheat resistor 98 to the condition of charge dependent upon the setting of the weld resistor 99.

Thus, during the preheat period, the unidirectiona1 voltage appearing across capacitor 94 steadily increases. The voltage of the capacitor 94 plus a reference voltage appearing between the conductor I2 of the direct-current control voltage supply and the adjustable tap88 of the voltage-dividing resistor 89 is impressed on the conductors 92 and 83 and through switch 82 on conductors 62 and 63. With the reversing switch 92 in the position indicated in the drawings, the variable component of voltage supplied by capacitor 94 is applied in a positive sense with respect to the control members of electric valves 48 and 49. As is well understood by those skilled in the art, an increase in the magnitude of this positive unidirectional component of Voltage in cooperation with the lagging alternating-current component of voltage derived from the transformer 64 advances the phase position of the instant of conduction of the electric valves 49 and 49. Without going into detail, it is believed apparent that this advance will advance the phase of the peaked voltages induced in the windings 39 of transformer 49 which, through the operation of the firing valves I8 and I9, will increase the magnitude of the current supplied to the load circuit. Therefore, theincreasing charge on the capacitor 94 during the preheat interval will provide a steadily increasing magnitude of load current. As previously mentioned, the rate of charge during this interval and, therefore, the rate of increase of load current depends upon the setting of th preheat timing resistor I29. The preheat period is terminated by conduction of the electric valve I39 which is initiated when the charge on the capacitor 94 corresponds to the setting of the tap I26 of the weld-heat resistor 99, since the'com trol member of valve I39 is maintained at substantially the voltage of the positive terminal of the capacitor 94 and the cathode of electric valve I39 is connected directly with the adjust able tap I26 on the weld-heat resistor 99. Thus, after the initial and final values of preheatcurrent have been adjusted by the adjustable taps WI and I26 of the resistors 99 and 99, the preheat t-imingresistor I29 provides means for independently adjusting the length of the preheat period. i

I When the valve I39 conducts at the end of the preheat period, the relay I44 is picked up as a result of its energizing winding I43 being 0011'.-

V initiate another period of load current. Closure nected in the anode-cathode circuit of the elec tric valve I39. The operation of relay I44 opens M41) alter the connections of the conductor 86 with the preheat and Weld resistors 98 and 99. These changes are important in connection with current patterns B and D when switch 81 is in the left-hand position and will be discussed at a later point in the specification. Contacts MM and I44e shunt the manual switches 299 and 29I, respectively, and are effective only when these. switches are open for pulsation welding. During the weld period, valve I39 continues to conduct and capacitor 94 is maintained charged to a voltage dependent upon the setting of the tap I26 of the weld resistor 99 and the current supplied to the load circuit during the weld period is determined by this setting. At the expiration of the period ior'which the weld timer I49 is adjusted, the valve I69 thereof conducts and the operating coil I59 of the weld-timer relay I5I is energized to close contacts I5Ia, I5Ib, I5Id, and to open contacts I5Ic. Closure of the contact I5Ia which is in shunt with the initiating contact I440 seals in the weld-timer initiating circuit. The closure of contact I5Ib initi I52. Opening of contact I5Ic opens the energizing circuit of the relay 26 and thereby termi-' nates the supply of current to the load circuit by interrupting the circuit of the control members of the main electric valves I2 and I3 by opening the contacts 29a. The closure of contact I5Id partially completes an energizing circuit for the operating coil II9 of the relay H8. It will be noted that closure of contact I 5Id will effect energization of the coil II9 if the contact I55a of the manual switch I55 is closed. As will be explained later, switch I55 is closed when it is desired to reduce the off-period time to zero.

After the expiration of the period for which the off-period timer is set, the operating coil I53 of the off-period timer relay I54 is energized to close the contacts I54a, I541), and I540, Closure of contact I54a completes an energizing circuit for the coil II9 of relay II8 from-the supply lines and 31. Closure of contact I54b completes an'energizing circuit for the operating coil 26 of the relay 2! to close contact 26a to of contact I540 completes a shunt circuit around the timing capacitor I89 of cool-period timer I63 to preclude any possibility of the cool timer from extending the off period beyond the time. for which the off-period timer is set by momentarily picking up the cool-timer relay I92.

As previously mentioned, closure of contact I-54a establishes an energizing circuit for the operating-coil II9 of relay IE8 to effect the operation of contacts H811 to H87, inclusive. Contact II8a closes to complete the connections of the operating coil I29 of the relay I2I inthe anode-cathode circuit of the valve I39. Contact Ii8b opens to interrupt the charging circuit of capacitor 94 through the preheat timing resistor I29 and contact IISd closes to establish another charging circuit for the capacitor 94 through the postheat timing resistor I58. Contact opens to drop out relay I44 to accomplish circuit changes which will be discussed at'a later time in connection with current patterns B and D'.

Contact II8e closes to complete a circuit from the postheat resistor I to the control member of electric discharge valve II2. Contact I-I8,f closes to complete a circuit with the postheat resistor I00 which is of significance in connection with patterns B and D. Contact I I8g, which shunts contact I'Ib, closes to seal in' the on timer I52. Contacts HM and H81 are connected in shunt with certain of the manual switches 200, MI, and 202 and are of interest in connection with the operation of the system for pulsation welding as has been previously described. Contact Il8g opens to permit the cool timer I63 to reset.

As mentioned above, closure of contact I IBd completes a circuit for the capacitor 94 through which the capacitor charges to a voltage dependent upon the setting of the tap I51 of the postheat resistor I00 and at a rate depending upon the setting of the postheat timing resistor I58. The control member of the electric valve H2 is connected with the postheat resistor and the cathode thereof is connected with the positive terminal of the capacitor 94 so that the valve H2 is rendered conductive when the voltage of the capacitor corresponds to the setting of the tap I5! of the postbeat resistor. Thus, the setting of the postheat timing resistor I58 determines the duration of the postheat period once the weld-heat and postheat resistors have been adjusted to establish the desired magnitude of weld current and final postheat current, As soon as electric valve II'2 conducts,- the operating coil I of relay I2I is energized to open contact I2Ia which. in turn, deenergizes the operating coil I91 of the relay I06. The opening of contact IIlBb deenerg'iies the operating coil 21 of the relay 26 to terminate the supply of current to the load circuit. Opening of contact I96b also deenergizes the weld timer I49. If the initiating switch is now opened, the relays H8 and I2I are dropped out and the relay I54 of the off-period timer is dropped out and the system is returned to its initial condition, the capacitor 94 being returned to a condition of charge dependent upon the setting of tap IOI of the preheat resistor 98. During the postheat period, the decrease in voltage of the capacitor decreases the positive unidirectional voltage component impressed on the control members of the electric valves48 and 49 to retard gradually the phase position of the instant of ignition of the main electric valves I2 and I3 to reduce gradually the magnitude of the current supplied to the load circuit.

When it is desired to supply a current pattern to the load circuit corresponding to the pattern of Fig. 2C, the reversing switch 82 is moved to the right-hand position. This reverses the D0- larity of the variable unidirectional voltage impressed on the control members 48 and 49 due to the capacitor 94' which now appears as a negative control voltage component. With the switch in this position. an increasein the voltage of the capacitor 94 retards the phase of the voltages induced in the windings 39 of transformers 40 and, thereby, gradually reduces the magnitude of the current during the preheat period and gradually increases it during the postheat period as illustrated in Fig. 2 by the curve designated Pattern C.

In the preceding description of the operation of the system, an off-period has been provided between the weld period and postheat period. This ofi period has a duration which is adjustable by adjusting the off-period timer I52. If

. period timer.

it is desired to omit the off period entirely, the manual switch I is closed, thereby closing contacts I55a and I550 and opening contacts I551). The opening of contact I55b disables the oil- The closure of contact I55a completes an energizing circuit for the operating coil I I 9 of the relay I I8 as soon as the relay I 5|, controlled by the weld-period timer, is closed, The closure of contact I55c maintains the operating coil 21 of the relay 26 energized when the weldperiod timer times out so that the load current is not interrupted.

In many applications, it is unnecessary that the magnitude of the current be varied during the diflerent intervals of the load-current pattern. The illustrated embodiment of the present invention may be readily adjusted to provide a loadcurrent pattern in which the current is of constant magnitude during each period but which is independently adjustable in magnitude for the diflerent periods. The system is adjusted for this type of operation by moving the single-pole switch 81 to the left and moving the switching device I04 to the right. Otherwise, the switches are placed in the same positions as described in connection with the current pattern A. This places the system in condition to produce the current pattern illustrated in Fig. 2B. The operation of the systern is in general very similar to that. described in connection with current pattern A with the exception that capacitor 94 is now required to time the preheat and postheat intervals only and isnot necessary for establishing the bias control voltage supplied to the control members of electric valves 48 and 49 during Preheat and postheat periods. Inasmuch as the capacitor 94 is not now utilized as a source of bias voltage, the timing of the preheat and postheat periods may be more completely separated from the adjustments of load-cur rent magnitudes so that it will not tie-necessary to readjust the preheat and postheat timing resistors I29 and I58, respectively. when it i desired to adjust the current level during these periods. This is accomplished by the switch I04 which, when moved to its right-hand position, connects the control member of valve I I2 through contacts I03 and I031) with an adjustable tap I50 on resistor 95. The contact I83a when moved to the right disconnects the cathode of the electric valve I30 from the adjustable tap I26 of the weld=heat resistor 99 and connects it with an adjustable tap- I6I on the resistor 96. The operation of the systern in supplying pattern C will now be very briefly reviewed. The initiating switch I55 is closed, relay I06 is energized, the relay I92 controlled by the cool-period timer I63 picks up momentarily to complete the circuit for the operating coil 21 of the relay 26. This initiates a period of energization of the load circuit. The magnitude of the current during the first or preheat period of the current pattern is determined by the setting of theadjustable tap IIlI of the preheat resistor 98 Which is, at this time, connected with the conductor 62 through the normally closed contacts M41; or the relay I44, the conductor 86, switch 81, and t e left-hand contact of switch 82. The magnitude of current determined by the setting of tap IIlI i supplied to the load circuit until the electric valve I30 is rendered conductive as a result of the capacitor 94 charging through the preheat timing resistor I29 to substantially the voltage of the adjustable tap IBI. Conduction of the electric valve I30 operates the relay I44 to open the connection between the adjustable tap IIH of the preheat resistor 98 and complete a circuit from the conductor 62 through the contacts 14417 to the adjustable tap I26 of the weld-heat resistor 99. The operation of the system during the welding period and the ofi period is substantially the same as that described in connection with current pattern A. At the end of the off period, relay I I8 is energized to close control H8) and relay is dropped out to open contact lMb. This disconnects the conductor 62 from the weld-heat resistor 99 and connects it with the adjustable tap [51 of the postheat resistor I00. The postheat timing is accomplished in the same general manner as before by the time required for. the capacie tor 94 to charge through postheat timing resistor I58 to a value which will render electric valve 1 l 2 conductive to energize the relay |2I to terminate the period of energization of the load circuit. This is determined now by the setting of tap I60 on resistor 95.

Pattern D is obtained by moving the switch 82 to the right and leaving the remainder of the manual switches in the same position as just described in connection with pattern B. In this way, the increase in unidirectional voltage which results from transferring the conductor 62 from the preheat resistor to the weld-heat resistor effects a retardation in the phase of the voltages induced in the secondary winding 39 of the transformer 40 and reduces the magnitude of the load current during the weld period. Otherwise, the operation is very similar to that previously described.

It has previously been mentioned that pulsation welding, that is, intermittent energization of the load circuit, during any one or all of the periods of each pattern may be obtained by selectively opening switches 200, MI, and 202 which permit the heat and cool timers to function in the manner described in detail earlier in the specification. If switch 200 is opened, pulsation welding is ob-: tained during the preheat period. As soon as the load is energized, the heat timer I62 starts a timing operation and, when the period expires, relay I90 is operated to open contact IBM and thereby interrupt the circuit of the operating coil 21 of the relay 26. When relay '26 drops out, contact 26a interrupts the circuit of the control members of the main electric valves to interrupt the energization of the load circuit. The closure of contact 260 upon deenergization of the winding 2'! initiates the operation of the cool-period timer 153, which functions to reestablish a circuit for the winding 21 of the relay 26 after the expiration of the period for which it is adjusted. Thus, the load circuit is alternately energized and deenergized during the preheat period when switch 200 is open for periods depending upon the time settings of the heat and cooltimers I52 and IE3. Inasmuch as the relay M4 is energized at the expiration of the preheat period, the contact l-Mb thereof will complete a circuit from conductor 203 through switches'20l and 202 to conductor 204 and thereby preclude the intermittent energization of the load circuit under the control of the heat and cool timers during the weld period. The contact H82 keeps this circuit completed during the 'postheat period as long as switch 202 is closed. In a similar way, pulsation welding may be effected during the weld period by opening only switch 2M and during the postheat period by opening switch 202 only. It will be apparent that any two or all of the switches may e opened if pulsation welding is desired during any two or all of the periods of the current patterns. If it is desired to obtain pulsation welding during more than one of the periods 0i t e current pattern, the heat and cool timers may be arranged to operate for difierent intervals during the different periods of the load current pattern. This may be accomplished by automatically changing the parameters or the timing circuits in accordance with the period of the load current being supplied. This type of control of timing circuits is described in detail and claimed in my copending application Serial No, 460,239,

load circuit which are made up of a plurality of independently adjustable periods of energization during each of which a particular current level or variation of current level is maintained. It will be noted that, in each of the patterns, a pattern of unidirectional control voltage corresponding to the desired pattern of load current is established by means of adjustable taps on the V current-dividing resistors which are selectively connected in circuit with a pair of control electric valves. When the system operates to produce patterns A and C, the voltage between these settings is gradually varied during the period to give a gradual change in load current. When any of the current patterns are being supplied, the voltage existing between difierent pairs of taps on the voltage-dividing resistor are successively'impressed on the control members of a pair of electric valves in accordance with the operation of the various timing means. The electric valve H2 controls not only the initial charge on the capacitor 94 but also the final charge thereon.

While.the illustrated embodiment of my invention relates to a spot-welding system in which the electrodes remainstationary throughout the duration of the current pattern, it'will be appreciated that many features of my invention are applicable to other systems such as those employed for seam welding. While the difierent periods of each of the current patterns have beenreferred to as preheat period, weld period, and postheat period, it will be understood that welding or heat treating may be accomplished during any one or all of the periods if desired and that, with the off period reduced to zero, the current pattern may represent the current pattern for a seam weld.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications'may be made without departing fronrmy invention in its broader aspects, and I, therefore, aim in the appended" claims to cover all suchchanges and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a supply circuit, a load cir-' cuit, electric translating apparatus interconnect ing said circuits including electric valve means, control means for controlling the conductivity of said electric valve means, means for energizing said control means with a unidirectional compoestablishing the initial value of said unidirectional component of voltage to establish the initial rootmean-square value of current transmitted to said load circuit at a finite value, means for establishing the final value of said unidirectional component of voltage to establish. the final root-meansquare value of current transmitted to said load circuit at a finite value, and. means responsive to the attainment of said final value for terminating said period of energization 2. In combination, a supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means, control means for controlling the conductivity of said electric valve means, means for energizing said control means with a unidirectional component of voltage comprising capacitance means, means for establishing an initial charge on said capacitance means while said valve means is nonconducting to determine the initial value of. current supplied to said load circuit, means for establishing a charging circuit for said capacitance to charge said capacitance means to a predetermined voltage to determine the final value of said load current including means for impressing a voltage of substantially greater magnitude on said chargingmeans than said predetermined voltage, means for determining the charging rate of said capacitance to determine the rate of change of the root-mean-square value of current in said load. circuit and the length of the interval between the initial and final values of said load current and means responsive to the charging of said capacitance means to said predetermined voltage for terminating said period of energization ofv said load circuit.

3. A control circuit for producing a predetermined pattern of unidirectional control voltage comprising a source of direct-current voltage, voltage-dividing means energized from said direct-current circuit for establishing a plurality of points of different potential relative to the terminals of said direct-current source, a. pair of output terminals, circuit-con-trolling means for altering circuit connections between said output terminals and said points to impress the voltage between different pairs of said points on said output terminals, and independently adjustable timing means for determining the interval between each successive alteration of said circuit connections to determine the portionof the total pattern that the voltages of the different pairs of points are impressed on said output terminals.

4. A control circuit for producing a. pattern of unidirectional control voltage having a plurality of periods comprising a source of direct-current voltage, a pair of output terminals, voltage-dividing means energized from said source of directcurrent voltage for establishing a plurality of points of diilerent potential relative to the terminals of said direct-current source, a plurality of circuit-controlling means for altering the circult connections between said output terminals and said points to impress the voltage between different pairs of said points on said output terminals, a capacitor, means for controlling the rate of charge of said capacitor between. an initial value and a second value to determine the time of operation of certain of said circuit-controlling means to terminate one period of said pattern, independent timing means for eifecting operation of other of said circuit-controlling means to establish the length of a second period of said pattern, and means for controlling the charging rate of said capacitor to a third condition of charge to effect the operation of still other of said circuitcontrolling means to determine the length of a third period of said pattern of voltage.

5. In combination, a supply circuit, a, load circuit, electric translating apparatus interconnectin said circuits including electric valve means, a control member for controlling the conductivity of said electric valve means, means for pro-establishing a plurality of different patterns of control voltage each including a plurality of intervals during which the control voltage is controlled in a predetermined manner, and means for impressing on said control member the voltage of a selected one of said patterns to eilect the transmission of a corresponding pattern of current to said load circuit.

6.v In. combination, a supply circuit, a load circuit, electric translating apparatus interconnecting; said circuits including electric valve means, a control member for controlling the conductivity of said electric valve means, means for establishing a plurality of diflcrent patterns of unidirectional control voltage each of which comprises a plurality of intervals of diflerent voltage magnitudes, said patterns of voltage differing from one another in the type of voltage variation during certain of the intervals of. each of the patterns, means for selectively impressing one of said patterns of control voltage on said control member to effect the energization of said load circuit with a current pattern corresponding to the pattern of unidirectionalvoltage impressed. on said control member,

7. In combination, a supply circuit, a loadv circult, at least one of said circuits being an alternating-current circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control member, a source of direct-current voltage, voltage-dividing means energized from said source oi direct-current voltage for establishing a plurality of points of diflerent potential relative to said direct-current source, and means for successively impressing the voltage between different pairs of said points on said control member at predetermined times during said interval to control the conductivity of said electric valv means and thereby effeet the energization of said load circuit with current the root-mean-square value of which is maintained at different constant values during successive portions of said interval.

8. In; combination, a supply circuit, a load circuit, at least one of said circuits being an alternating-current circuit, electric valve means interconnecting said circuits for controlling th transfer of current therebetween, a control member for controlling the conductivity of said electric valve means, means for energizing said control member including means for impressing thereon a unidirectional voltage of predetermined magnitude for a predetermined interval of time, means for maintaining said electric valve means non-conductive for a succeeding interval of predetermined duration, and means for subsequently impressing on said control member a unidirectional voltage of a second predetermined magnitude for energizing said load circuit for a second interval of time with a current of a different magnitude.

9, In combination, a supply circuit, a load circuit, at least one of said circuits being an alternating-current circuit, electric valve means interconnecting said circuits. for controlling the transfer 01' current therebetween, a control member for controlling the conductivity of said electric valve means, means for impressing on said control member a unidirectional voltage for a predetermined interval of time, means for maintaining said electric valve means non-conducting for a succeeding interval of predetermined adjustable duration, meansfor subsequently impressing on said control member a unidirectional voltag of progressively varying magnitude for a second predetermined interval of time to energize said load circuit for two different intervals with currents of diflerent magnitudes and one of which varies progressively in magnitude with a period of deenergization of predetermined duration separating said periods of energization.

10. In combination, an alternating-current supply circuit, a load circuit, electric translating apparatus interconnecting said circuitincluding electric valve means connected to transfer a predetermined pattern of alternating current between said supply and load circuits, a control member for controlling the magnitude of the current supplied to said load circuit, a source of direct-current voltage including means for establishing a plurality'of points of different potential relative to the terminals of said direct-current source, circuit connections between difierent pairs of said points and said control member including circuit controlling means, and means for operating said circuit-controlling means to impress the voltage between difierent pairs of said points on said control member in succession, and timing means for determining the interval between successive alterations of said circuit connections to determine the portion of the total pattern of load current thatthe potentials of the different pairs of points are impressed on said control member to maintain the current supplied to said load circuit at a value corresponding to the potentials of said different pairs of points during the difierent portions of saidpatterns. A

11. In combination, a supply circuit, a load circuit, at least one of said circuits being an alternating-current circuit, electric translating ap paratus interconnecting said circuits, including electric valve means having a control member, a capacitor, means for charging said capacitor between' pre-established finite values of charge, means responsive to the voltage of said capacitor for gradually varying the instant in the voltage wave of said alternating-current circuit that said electric valve means conducts as the charge on said condenser changes, and circuit-controlling means operated in accordance with the voltage of said capacitor to terminate a period of energization of said load circuit when said capacitor attains a predetermined value of charge, whereby the charging of said capacitor controls boththe magnitude of the current supplied to the load circuit and theinterval of energization of the load circuit. v

12. In combination, a supply circuit, a load circuit, at least one of said circuits being an alternating-current circuit, electrictranslating apparatus interconnecting said circuits including electric valve means having a control member, acapacitor. means responsive to the voltage of said capacitor for energizing aid control member to vary gradually the instant in the voltage wave of said alternating-current circuit as said electric valve means conducts as the charge on said condenser changes, means for establishing a charging circ'uit for said capacitor to charge said capacitor between pre-established values to effect a period of energization of said load circuit with a current the root-mean-square value of which gradually changes between values determined by said pro-established values of charge on said capacitor, means fordetermining the rate of charge of said capacitor to'determine the duration of said period of energization of the load circuit and timing means initiated in operation when the load current reaches the second of said predetermined values for determining th duration of a second period of energization of said load circuit.

13. In combination, a supply circuit, a load circuit, at least one of said circuits bein an alternating-current circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control member, a capacitor, means responsive to the voltage of said capacitor for energizing said control member to vary gradually the instant in the voltage wave of said alternating-current circuit as said electric valve means conducts as the chargeon said conthe rate of charge of said capacitor to determine the duration of said period of energization of the load circuit, and means for altering the charging circuit of said capacitor to initiate charging of said capacitor to stillanother pre-established value to effect the energization of said: load circuit for a second period dependent upon the charging rate of said capacitor to said last-mentioned preestablished value and with a current the rootmean-square value of which gradually changes from said final value of said first period to the value determined by said last-mentioned preestablished value.

14. In combination, a source of direct-current voltage, means establishing a plurality of points of different potential relative to the terminals of said direct-current source, an electric valve including an anode, a cathode, and a control member, a capacitor connected to the cathode of Said electric valve and to said direct-current source, switching means connecting said control member with one of said points of potential to establish a charge on said capacitor, means for operating said switching means to interrupt said charging circuit and for establishing a second charging circuit for said capacitor, mean for subsequently connecting said control member with a second of said'points of potential to render said electric valve conductive when the charge on said capacitor reaches a predetermined value with respect to said second point of potential.

j15. In combination, a source of direct-current voltage, means establishing a plurality of points of difierent potential relative to the terminals of said direct-current source, a capacitor, an electric valve including an anode, a cathode, and a control member, means including switching means connecting said capacitor in a chargin circuit including the voltage between a pair of saidpoints and the control-n1ember-to-cathode circuit' of said electric valve, means for initiating a timing period including means for establishing a second charging circuit for said capacitor and interrupting the charging circuit including th control member of said electric valve, means includin a second electric valve having a control member energized in accordance with the voltage of said capacitor for interrupting said second charging circuit when said capacitor reaches a second condition of charge and establishinga third .charg ing circuit for said capacitor, means for connecting the control member of said one lectric valve with another of said points of potential to render said one electric valve conducting when said capacitor reaches a third condition of charge, and means responsive to the operation of said one electric valve for terminating the timing period.

16. A control circuit comprising a source of direct-current voltage, voltage-dividing means energized from said source of direct current for establishing a. plurality of points of potential relative to the terminals of said direct-current source, a capacitor, an electric valve including an anode, a cathode, and a control member, means establishing a charging circuit from one of said points including the control-member-to-cathode circuit of said el ctric valve to establish an initial charge on said capacitor, a second electric valve including an anode, a cathode, and a control member, means connecting the cathode of said second electric valve to a second of said points, means connecting the control member of said second electric valve to one of the terminals of said capacitor so that said second electric valve is rendered conductive when said capacitor reaches a predetermined voltage relative to said second point of potential, means responsive to conduction of said second valve for establishing a charging circuit for said capacitor to a third condition of charge, said first electric valve being arranged to become conductive when said third condition of charge is obtained to interrupt the charging circuit of said capacitor, the charging rate of said capacitor between said first and second and second and third conditions of charge being independently adjustable to determine the interval of each of the charging periods of said capacitor.

17. In combination, a source of direct-current voltage, means establishing a plurality of points of different potential relative to the terminals of said direct-current source, a pair of lectric valves each including an anode, a cathode, and a control member, a capacitor, one terminal thereof connected with the cathode of one of said electric valves and with the control member of the other of said electric valves, mean for establishing a circuit for charging said capacitor from said direct-current source, means connecting the cathode of said other electric valve to one of said points of potential so that said other electric valve is rendered conductive when said capacitor reaches a predetermined condition of charge, means operated in respons to the conduction of said other electric valve for interrupting said charging circuit and establishing a second charging circuit for said capacitor, means connecting the control member of said first electric valve with another of said points of potential so that one electric valve is rendered conductive when said capacitor reaches a second condition of charge, and means for adjusting the charging rate of said capacitor in each of said charging circuits to determine the interval required for each of said charging operations.

18. In combination, a supply circuit, a load circuit, electric translating apparatus interconnecting said circuits including electric valve means, a control member for controlling the conductivity of said electric valve means, means for energizing sait. control member with a control voltage having a predetermined pattern for efiecting th energization of said load circuit for a plurality of intervals during which diflerent current magnitudes are supplied to said load circuit, a pair of independently adjustable timing means, and

means for rendering said timing means effective to modify the energization of said control memher to sheet intermittent energization of said load circuit during any of said intervals, the adjustments of said timing means determinin the relativ durations of the periods of energization and .deenergization of said load during the intervals that said timing means is effective.

19. In combination, an alternating current supply circuit, a load circuit, electric translating apparatus interconnecting said circuit including electric valve means having a control electrode, means for controlling the energization of said control electrode to determine th magnitude of the current transmitted to said load circuit and timing means for establishing a plurality of intervals during which said load circuit is to be energized including a capacitance, means for establishing an initial charge on said capacitance, means for establishing a, charging circuit for charging said capacitance to a second value, means responsive to the charge on the capacitance for effecting a circuit controlling operation at the end of the interval required for said capacitance to charge to said second value, means for establishing a second charging circuit for said capacitance to charge the capacitance to a third value of charge, and independently adjustable resistance means, in each of said charging circuits for determining the time required for the capacitance to charge between said different values of charge.

20. In combination, a supply circuit, a capacitance, means for establishing a charging circuit for charging said capacitance from said supply circuit to change the voltage on said capacitance irom an initial value to a second value, an electric valve responsive to the attainment of said second voltage for accomplishing a circuit controlling operation, means for establishing a second charging circuit for said capacitance to charge said capacitance to a third voltage, an electric valve responsive to the attainment of said third value of voltage on said capacitance lior accomplishing a second circuit controlling operation, and independently adjustable resistance means in each of said charging circuits for controlling independently the time intervals required for accomplishing said first and second circuit controlling operations.

21. In combination, a supply circuit, a load circuit, at least one of said circuits being an alternating current circuit, electric valve means interconnecting said circuits for controlling the transfer of current therebetween, a control member for controlling the conductivity of said electric valve means, means for energizing said control member to efl'ect tne transmission of current or a predetermined magnitude to said load circuit for a predetermined interval, timing means including a capacitor and an electric valve for controlling the duration of said interval, a second timing means for maintaining said electric valve means nonconducting for a second predetermined interval, means for impressing a control voltage on said control member to ell'ect transmission of current of diiferent magnitude to said load circuit during a third predetermined interval, and means including said capacitor for determining the duration of said third interval.

22. In combination, a supply circuit, a load circuit, at least one of said circuits being an alternating current circuit, electric translating apparatus interconnecting said circuits including electric valve means having a control member, a

sourceof direct current voltage, voltage dividing means energized from said source of direct current voltage for establishing a. plurality of points of different potential relative to said direct current source, a plurality of. electronic timers each including an electric valve and, a capacitor for impressing the voltage between different pairs of said points on said control member at predetermined times during said interval to'co'ntrl the conductivity of said electric valve meansJand thereby effect the energization'of said load-circuit with current wtheflroot-mean square value of whichis maintained at different constant. values during different portions of said interval.

, f MAURICE EBIVEN 

